If I were you, simply replace your stiff springs with something a little more plush. A lot of guys will put in a road race spring at all 4 corners which is cool, but if you daily drive your stang it can become tiresome pretty quick. Don't put in air shocks, airshocks are for vehicles that take on heavy loads in the rear so you add more air to compensate for the added weight OR 79' camaros or el caminos with jacked up rear ends lol. Air ride shocks are not too pricey, but all the supporting hardware is...regulators, air tanks, lines, fittings, install. It can easily approach $1000+ quickly. Get some softer springs and call it a day